Custom Swimwear Manufacturing Guide: Fabric, Sizing & MOQ

Swimwear is the most technically demanding category in activewear. A yoga pant needs to stretch. A running shoe needs to cushion. But a swimsuit needs to do both — while submerged in chlorinated water, exposed to UV radiation, stretched to 150%+ over the body, and then do it all again the next day for an entire season.

Get the fabric wrong, and the suit becomes see-through when wet, loses its shape after 10 pool sessions, or the colors fade to pastel within weeks. For retailers, swimwear has one of the highest return rates in apparel when quality isn't dialed in — and the #1 complaint is always the same: "it went see-through in the water."

This guide covers every technical decision that goes into wholesale custom swimwear — fabric blends, chlorine resistance, UPF testing, printing methods, lining requirements, and MOQ tiers — with real numbers from our production floor.

1. Why Swimwear Is the Most Demanding Category in Activewear

Before diving into specs, it's worth understanding why swimwear manufacturing is fundamentally different from other activewear:

• Chemical exposure: Pool chlorine is one of the most destructive substances for textiles. It breaks down spandex at the molecular level, causing embrittlement and loss of stretch. Regular spandex degrades in 50-100 hours; chlorine-resistant variants last 300-500 hours.
• Wet-state performance: Swimwear must perform when saturated with water. Fabric that's opaque when dry can become transparent when wet. Seams that hold dry can weaken when soaked.
• UV exposure: Outdoor swimwear is exposed to intense, direct sunlight — often reflected off water surfaces. UV degradation causes color fading and fiber weakening.
• Extreme stretch: Swimwear is stretched to 150-200% when worn. The fabric and seams must maintain integrity under constant tension — in water, which adds drag forces.
• Skin contact sensitivity: Swimwear is worn directly against sensitive skin areas. Lining requirements, chemical compliance, and seam placement are more stringent than outerwear.

These five factors are why swimwear has higher fabric costs, more rigorous testing requirements, and longer production cycles than most activewear categories.

2. Fabric Blends: Nylon vs. Polyester vs. PBT

Swimwear fabrics fall into three main categories, each optimized for different use cases:

Nylon-Spandex: The Comfort Choice

Nylon-spandex (80/20 or 78/22) is the most popular choice for casual and fashion swimwear. It has a softer hand-feel than polyester, drapes beautifully on the body, and provides excellent comfort for beach and poolside wear. The trade-off: nylon is less chlorine-resistant than polyester, so it's best suited for occasional swimmers and fashion-focused buyers.

Polyester-Spandex: The Performance Choice

Polyester-spandex (82-88% / 12-18%) is the standard for competitive and training swimwear. Polyester is inherently more chlorine-resistant than nylon, and when paired with chlorine-resistant spandex (see Section 4), it creates a fabric that can withstand hundreds of hours in chlorinated pools. It's also more UV-resistant and holds color better over time.

PBT: The Extreme Durability Choice

PBT (polybutylene terephthalate) is a specialty fiber that offers the highest chlorine resistance of any swimwear fabric. It's essentially immune to chlorine degradation — PBT fibers maintain their stretch and strength even after 500+ hours of pool exposure. It's used for competitive suits that need to last an entire season of daily training, and for water polo uniforms that face extreme mechanical and chemical stress.

Eco Option: rPET

Recycled polyester (rPET) + spandex is available for brands with sustainability commitments. GRS (Global Recycled Standard) certified. Performance is comparable to virgin polyester-spandex.

3. The Spandex Ratio: Why 20% Is the Golden Number

Spandex (elastane) content is the single most important factor in swimwear performance. Too little, and the suit doesn't hold its shape or provide compression. Too much, and the fabric becomes unstable and expensive.

The "golden ratio" of 20% spandex hits the sweet spot: enough to provide excellent shape retention and body-hugging fit, without the cost and instability of excessive spandex content. This is the spec we recommend for most brands unless they have a specific performance requirement (competition compression or luxury comfort).

Our Fabric Specs:Casual/Fashion: Nylon 80% + spandex 20% (or 78/22). Competitive/Training: Polyester 82-88% + spandex 12-18%. Extreme Chlorine: PBT + spandex or 100% PBT. Eco: rPET + spandex (GRS certified). Weight: 180-230 GSM (competitive 200-230, casual 180-200). Premium chlorine-resistant: Nylon + XLANCE® / LYCRA® XTRA LIFE™ / CREORA® Highclo™.

4. Chlorine Resistance: The Make-or-Break Performance Metric

Chlorine resistance is what separates a swimsuit that lasts one season from one that lasts five. Here's the science:

Chlorine in pool water attacks spandex at the molecular level, breaking the polyurethane chains that give the fiber its stretch. Regular spandex starts to embrittle after just 50-100 hours of chlorinated water exposure. The suit loses its shape, becomes baggy, and eventually the fabric tears easily.

Testing Standards

Performance Benchmarks

Chlorine-Resistant Spandex Brands

For brands that need guaranteed chlorine resistance, we offer three certified spandex options:

• LYCRA® XTRA LIFE™ — the industry benchmark; lasts 3-5× longer than regular spandex in chlorine
• CREORA® Highclo™ (Hyosung) — Korean chlorine-resistant spandex; excellent value-to-performance ratio
• XLANCE® — premium chlorine-resistant fiber for high-end swimwear

All branded fibers are confirmed in writing before production. Regular spandex degrades in 50-100 hours; these specialty fibers last 300-500 hours — a 3-5× improvement.

Buyer's Tip: If you're selling swimwear for lap swimmers, swim teams, or anyone who trains regularly in chlorinated pools, insist on chlorine-resistant spandex. The cost premium is 15-25% over regular spandex, but it's the difference between a suit that lasts 3 months and one that lasts 12+ months. Your customers will notice — and so will your return rate.

5. UPF 50+ Protection: Standards, Testing & Legal Claims

For outdoor swimwear, UPF (Ultraviolet Protection Factor) rating is not just a feature — it's a legal claim. You can't just say "sun protection" without meeting specific testing standards.

International Standards

Why ASTM D6544 preconditioning matters: This standard requires the fabric to be simulated for wear (stretching, wetting, and abrasion) before UPF testing. A fabric that tests UPF 50+ when new might only test UPF 25 after stretching and wetting — which is what actually happens when someone wears a swimsuit. Preconditioning ensures the UPF rating reflects real-world use.

Our UPF Standard: All swimwear achieves UPF 50+ (>98% UVA/UVB blockage), tested per AATCC TM183 with ASTM D6544 preconditioning. We test to multiple international standards (AS/NZS 4399, EN 13758, GB/T 18830) depending on your target market.

6. Printing Methods: Sublimation vs. Acidic DTG vs. DTF

The printing method depends on the fabric fiber — polyester and nylon require completely different printing chemistry:

Sublimation on Polyester

Sublimation is the gold standard for competitive swimwear printed on polyester. The process uses heat (185-190°C) and pressure (35-45 seconds) to convert solid ink into gas that bonds with the polyester fiber. The result: photographic-quality prints with>80 wash durability (AATCC 61). High-adhesion transfer paper is critical — cheap paper causes ghosting and color inconsistency.

Acidic Dye DTG on Nylon

Nylon can't be sublimated (the temperature required would damage the fiber). Instead, acidic dye direct-to-garment printing is used. This method sprays acid dyes directly onto the nylon fabric, which then bond chemically. It supports 10-12 colors in a single pass — ideal for the complex, multi-color prints popular in fashion swimwear.

File Requirements

All printing requires: AI or PSD files, 300 DPI minimum resolution, RGB color mode, with Pantone color references for matching. We verify color accuracy against Pantone standards before production.

7. Lining Requirements: Why the Hidden Layer Matters

Lining is the part of the swimsuit that touches sensitive skin. It's also where corners get cut by cheap manufacturers — and where quality matters most for customer satisfaction.

Our Lining Standards

• Standard lining: Same fabric as shell (nylon-spandex or polyester-spandex), double-layer construction. This provides opacity when wet and consistent stretch.
• Children's / sensitive skin: Pure cotton lining. Softer against sensitive skin, hypoallergenic, and breathable.
• Crotch lining: Mandatory on all swimwear. Must be a separate fabric panel — never mesh. Mesh is prohibited for crotch lining due to hygiene and comfort concerns.

8. Stitching: Competitive vs. Recreational Construction

Critical rule: All swimwear must use polyester thread — never regular nylon or cotton thread. Nylon and cotton degrade rapidly in chlorinated water, causing seam failure. Polyester thread maintains its strength throughout the suit's lifespan.

Competitive suits minimize seams to reduce drag in the water. Every seam is a potential point of resistance. Recreational suits prioritize comfort and cost-efficiency with standard flat seam construction.

9. Sizing: Women's, Men's & Children's

Children's swimwear must comply with GB 31701 (China's children's textile safety standard), which includes requirements for drawstring length, small parts, and chemical limits. Two-piece designs are recommended for children to facilitate easy dressing and bathroom use.

10. MOQ by Product Type: Bikini, One-Piece & Competitive

Swimwear MOQs vary significantly by product type due to differences in construction complexity and fabric requirements:

Flexible MOQ Options:Simple color changes: As low as 100 pcs. Sublimation printing: Typically 300+ pcs minimum (digital plate setup cost). Start-up brands: Reduced trial MOQs available. Group orders: Can go as low as 20-50 pcs per style when combining with other buyers.

Buyer's Tip: If you're launching a swimwear brand, start with recreational one-pieces or bikinis (200 pcs MOQ) rather than competitive suits (300-500 pcs). Once you've validated your market and sizing, expand into competitive or specialty styles. Sublimation printing MOQs (300+) are worth the commitment if you want all-over prints — the print quality and durability are significantly better than DTG for polyester fabrics.

11. Production Timeline & Lead Times

Our Lead Times:Sampling: 7-15 days (technical sample). Total production cycle: 35-60 days (fabric sourcing + production + QC). ~500 pcs: approximately 25-30 days for production. Rush orders: 15 days available with 20-30% surcharge. Shipping additional.

Why swimwear takes longer than other activewear: Specialty fabrics (chlorine-resistant spandex, PBT) have longer sourcing lead times. The lining adds a full extra construction step. Wet-state opacity testing and UPF testing add QC time that other categories don't require.

12. Frequently Asked Questions